SIP在互联网多媒体通信中的应用

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《Internet Multimedia Communications Using SIP》是一本专注于互联网多媒体通信领域的重要著作，特别关注Session Initiation Protocol (SIP) 的应用。SIP 是一种广泛应用于网络电话、视频会议和多媒体通信的标准协议，它允许用户在不同的网络环境中发起、控制和管理会话。该书详细探讨了如何利用 SIP 在 Internet 上实现高效、可靠的多媒体通信，包括语音通话、视频聊天、文件共享等服务。 SIP 的核心在于它的寻址机制，能够统一处理来自各种通信设备（如固定电话、移动电话、VoIP 软件）的多媒体请求。书中可能涵盖了 SIP 的工作原理，如何通过 URI 格式进行呼叫请求和响应，以及相关的信令流程。此外，作者可能会介绍如何设置和配置 SIP 服务器，包括注册、会话管理、安全措施等内容，以确保通信的稳定性和安全性。对于网络工程师、系统架构师以及多媒体通信领域的开发者而言，这本书是不可或缺的参考资料。它不仅教授理论知识，还可能包含实践案例和示例代码，帮助读者掌握如何在实际项目中部署和优化 SIP 基础架构。此外，书中可能还会涉及与其他通信技术（如蓝牙）的集成，以增强无线多媒体通信的能力。书中的内容还包括了其他相关主题，比如网络安全（如 Information Assurance），网络安全系统的可靠性和安全性，以及网络模拟实验的设计与分析。同时，对于 IPv6 的高级协议实施、网络分析、设计、路由算法和质量-of-service (QoS) 管理也有深入讲解，这些都是构建现代多媒体通信网络时必不可少的技术要素。总而言之，《Internet Multimedia Communications Using SIP》提供了一个全面的视角，从基础概念到实际应用，帮助读者理解和掌握如何利用 SIP 进行互联网多媒体通信，是提升网络技术和多媒体通信能力的宝贵资源。

Why This Book

In the late 1990s, I was engineering manager at the switching department in a

mobile telecom operator. The mobile switches we dealt with were based on

circuit-switched technology. They were big, complex, and proprietary pieces

of hardware and software involved almost exclusively in the provision of voice

service. By that time, ATM (Asynchronous Transfer Mode), a packet-switched

technology that followed the virtual circuit approach, started to gain maturity as

a suitable way for carrying media trafﬁ c with QoS requirements. Media transport

was only part of the problem. The other part, signaling, did not have, by then, a

mature candidate. The industry response was to strip the existing circuit switches

off their switching matrix and provide them with the interfaces to control an

external packet-based switching matrix in the so-called soft-switch approach. It

was kind of throwing out the old-fashioned hardware but retaining the software.

That was a pragmatic approach that the market took in order to rapidly respond

to the operator ’ s needs. However, it still took several years for the telecom

operators worldwide to implement these architectures. By that time, we knew

there was work in the IETF about a protocol called SIP, whose ﬁ rst version

was published in 1995, but the main focus of the industry was on H.323 for

enterprise networks and in the soft-switch approach for public telecom networks.

In the meantime, Internet and the web were increasing their popularity, but

this fact seemed, by then, unrelated to our challenge of evolving the network.

Being intrigued about the possibility of using a packet-based network for media

transport, that was the ﬁ rst time I built an IP soft-phone. I just developed a simple

Windows program over the Win32 API on a standard PC. I made up a simple

signaling protocol consisting of a bunch of messages and sent them over TCP/

IP using the Winsock interface. Regarding the media, I just got the raw voice

samples from the Wave API and put them directly on UDP packets that I sent over

the network using Winsock. Surprisingly enough, it worked, and I could test it

over a medium-sized LAN. I needed no voice network equipment (neither voice

switch nor soft-switch), just a dumb IP network and a Windows program that I

developed in a few weeks and ran on a cheap PC. The simplicity and the ﬂ exibility

of the solution convinced me that voice technology as we knew it was meant to

change sooner or later, and that the new technology would be one that advocated

simplicity in the network and ﬂ exibility in the endpoints as well as cheap and

off-the-self hardware and software.

In the next years, I changed roles and became manager for a team doing mobile

services design and development. By that time, I had already built a new version

of my softphone, only that then I used a beta version of a SIP stack, an Internet

protocol that was destined to revolutionize multimedia communications both in

the Internet and in the telecom environment. As will be explained in this book,

Preface

xvi

Preface

SIP follows the ﬂ exible Internet approach that advocates moving intelligence to

the endpoints and keeping the network as simple as possible.

During that time, I became convinced that understanding, even if it is at a high

level, how SIP software works helps to understand its simplicity, ﬂ exibility, and

potential. And that is the reason why, when years later I decided to write a book

on a state-of-the-art approach for multimedia communications, I went for an

approach that combined theory with practice. And the result is this book.

Approach

This book ’ s aim is to let readers understand what Internet multimedia

communications are and how they are enabled by using the Session Initiation

Protocol and other related technologies. The approach I have taken in writing

this book has three main characteristics.

First, it is Internet-orientated . That is, it is focused on the Internet technologies,

protocols, and practices for delivering these services. In the last two chapters, it

also touches upon how these Internet technologies can be used in controlled

network scenarios such as those present in telecom operators ’ multimedia

networks. In fact, the bodies involved in the standardization of telecom networks,

such as ETSI or 3GPP, have adopted the ideas coming from the Internet in order

to design the next generation of telecommunication networks.

Second, it follows a fully modern and up-to-date approach where the latest

Internet developments are analyzed and discussed. In addition to providing a

thorough explanation of the basic concepts, it also presents the most recent

proposals for utilization of SIP and related technologies in the remit of multimedia

communications. The book tackles new and innovative technologies and services

such as MSRP, NAT traversal, STUN, ICE, session border controllers, TCP-based media

transport, XCON conferencing framework, media server control, GRUUs, RPID,

latest approaches for RTP security, XCAP, Text over IP, remote call control, ﬂ oor

control, conference control, Fax over IP, enhanced identity management, IMS,

TISPAN next generation networks, voice call continuity, IMS centralized services,

and so forth.

Following a modern approach implies that the book contains not just references

to ofﬁ cial standard or informative documents (e.g., Request For Comments), but

also many references to the latest IETF Internet Drafts that represent current

work in progress.

Third, the book is unique in its kind by the fact that it not only contains theory

but also practice . The practical nature of the book is twofold. On one hand, the

book tackles multimedia service creation, both at SIP level and at media level.

It contains a comprehensive description of the state-of-the-art technologies

xvii

Preface

for multimedia service creation. More than that, the book explains in detail

how to program multimedia services using Java. Readers will learn how to

programmatically use an open-source SIP stack and a popular Java API for

media development. Many examples and Java practices are included in the book.

Readers are guided step-by-step to build a simple yet functional soft-phone

supporting voice, video, and messaging, plus a simple SIP proxy and registrar to

be used with the soft-phone. The main purpose for the inclusion of code in the

book is derived from my experience when dealing with multimedia technology:

being able to take a look, even if you are not a Java programmer, at code that

illustrates how services are done facilitates the comprehension of the technical

concepts and the simplicity and potential in the technology. Another aspect of

the practicality of the book refers to the fact that it also contains explanations

of the situations where the different technical solutions may be used in real

deployments.

Audience

The book is targeted at several types of audiences. In any case, all readers should

have a technical background, an interest in technology, or a passion for Internet-

related topics.

First, this book is targeted at the professional in the telecom or IT industry

who needs to gain an understanding of the newest Internet Protocol–based

technologies for delivering voice, video, messaging, and data services, and to

acquire the skills and tools to successfully design and implement multimedia

solutions in different environments (from small enterprise deployments up to

Internet-wide deployments). IT architects will use the book to understand how

their existing enterprise IP networks can be leveraged for delivering voice, video,

and messaging, and what technologies the products that they choose must

support. Telecom architects will use the book to gain an understanding of how

SIP and other Internet technologies can be used to evolve their networks and

offer innovative services (or offer existing services but with a reduced CAPEX

and OPEX!). SIP related technologies play a key role in the movement into Fixed

Mobile Convergence and Total Communication propositions that most telecom

operators are embracing nowadays. IT and telecom engineers will ﬁ nd the

necessary information in the book to understand how technology works, and will

be referred to the appropriate technical documents for further detail. The book is

also very useful for IT and telecom managers that want to understand how their

business needs to be evolved toward an all-IP infrastructure and what are the

beneﬁ ts and challenges in doing so.

Second, this book is targeted at the academic community, where it can be used

as base material for a one-semester theoretical course on Internet multimedia

communications or as support material for practices in a laboratory course.

xviii

Preface

Third, software developers will ﬁ nd in the book the necessary theoretical and

practical information that allows them to learn how to build basic SIP applications

and sets the grounds for more-complex application design and development.

And last but not least, any person who has a technical background and has a

passion for being informed about the hottest stuff around the Internet is also a

potential candidate for enjoying the book.

Organization

The book is organized in three parts and 24 chapters.

The ﬁ rst part, “ Fundamentals, ” comprises the ﬁ rst ﬁ ve chapters in the book. These

give the necessary background information on Internet multimedia architecture,

protocols, and service creation tools for understanding the rest of the book.

Above all, this ﬁ rst part explains the rationale behind the design of the multimedia

protocols and the remit in which they are used. Setting the scope of the technology

is crucial for using it successfully.

The second part, “ Core Protocols, ” is the central part of the book, and is dedicated

to explaining how the main protocols work in concert to deliver multimedia

services. In order to enhance the comprehension of the theory, the reader is

also guided into the elaboration of simple Java-based programming practices

that allow him or her to better comprehend the theoretical concepts. As part of

these practices, readers will learn to build, step-by-step, a simple yet functional

soft-phone supporting voice, video, and messaging. Those readers who are not

interested in the programming practice can simply skip the related chapters and

just focus on the theory. However, I would recommend that even these readers

take a quick look at some of the code snippets so that they can get a high-level

understanding of how applications can be developed.

The third part, “ Advanced Topics, ” deals with the latest and most innovative usages

of the technology. Readers who already have professional experience with the

technology, either designing or developing solutions, might want to skip the

ﬁ rst two parts and dive directly into this part. In addition to tackling the most

recent advances in the technology, Part III also shows how hot issues that every

multimedia deployment faces are resolved. An example of that is the hot NAT

traversal topic, of which a very thorough analysis is done and several possible

solutions are detailed.

Additionally, the last two chapters in the book explain how Internet multimedia

technology can be used in network scenarios where a tighter relationship with

the service provider exists. A paradigmatic example of this concept is the 3GPP

IMS, to which a long chapter is exclusively dedicated. The approach used in this

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Preface

book to present the IMS architecture and concepts is very different from the

traditional one used by other books on the subject. Instead of ﬁ rst introducing

an overwhelming architecture diagram full of unintelligible names and then

explaining what the role is of the various components, a different approach is

followed. It is based on leveraging the Internet concepts learned throughout

the book, and explaining how they naturally evolve to support additional

requirements that telecom operators may have, and that are not strictly relevant

in a pure Internet environment.

Code Examples

This book does not intend to teach programming. The code examples are

included just for the shake of illustrating how the protocols work. Readers

can build simple examples where they can test the concepts learned. I have

purposely omitted the bulk of error checking and recovery so as not to deviate

the reader ’ s attention from the functional concepts. I am convinced this has

resulted in more comprehensive programs that show clearly how protocols

operate. On the other hand, it means that programs are not ﬁ t for commercial

use, and that they need to be fed with consistent data; otherwise, they will fail.

Additionally, when I have thought that good OO practice made the functional

concepts more difﬁ cult to understand, I have preferred to sacriﬁ ce perfect OO

programming techniques.

Acknowledgments

I wish to thank Rogier Noldus, from Ericsson, and David Page, chief scientist

at OpenCloud, for their impressive work in reviewing the manuscript. Their

comments and suggestions have greatly contributed to the possible quality of the

ﬁ nal product. Also, Nick Hudson, a former colleague at Vodafone, reviewed the

manuscript and provided useful feedback. Santiago Borrero, a colleague of mine

at Vodafone, reviewed the ﬁ rst introductory chapters and contributed to making

the technical concepts in them easier to understand for readers with different

backgrounds.

I also want to thank Rick Adams, Greg Chalson and Mónica González de Mendoza,

my editors at Elsevier, who believed in the project from the very beginning and

who provided timely help and assistance that allowed us to overcome the hurdles

encountered during the manuscript delivery process.

My biggest thanks go for my wife, whose encouragement, support, patience,

and understanding have been crucial for the successful accomplishment of this

project.

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